Hitherto, a soft contact lens is softer rather than a hard contact lens and therefore the configuration of the soft contact lens is easy to deform under its own gravity in measuring optical characteristics while holding the soft contact lens in a lens receiver in air. When the soft contact lens includes a large quantity of water, the water in the soft contact lens evaporates while the soft contact lens is held in air a long time.
Accordingly, an error is easy to occur in measurement of the optical characteristic values for the soft contact lens in air and essence and quickness are required to measure the soft contact lens in air. A lens meter (refracting power measuring apparatus) is being developed to measure the optical characteristic values with holding a configuration of the soft contact lens which is dipped in water.
In the meter, because the optical characteristic values can be measured with holding the configuration of the soft contact lens and without evaporating water, the essence is not required. The optical characteristic values of the soft contact lens can, also, be measured without the quickness being required.
However, the optical characteristic values of the soft contact lens measured in liquid are different from that measured in air.
In optical characteristic values measured in liquid, a difference between refractive indexes of the soft contact lens and liquid is less than a difference between refractive indexes of the soft contact lens and air.
Accordingly, the optical characteristic values of the soft contact lens measured in liquid are less than that measured in air. As a result, the optical characteristics of the soft contact lens in liquid must be converted into that measured in air. A refractive index of material of the soft contact lens is required to this conversion.
However, the refractive index of material of the soft contact lens is almost unknown in general. Thus, it is not able to correctly convert the optical characteristic values measured in liquid into the optical characteristic values in air which represent optical characteristic values of a soft contact lens which is worn in eye. As a result, there is a problem in which reliability of the converted optical characteristic values obtained by converting the optical characteristic values measured in liquid is lack.
It is an object of the present invention to provide a refracting power measuring apparatus in which optical characteristic values of a soft contact lens can be precisely measured in air.